Image reading devices such as facsimiles, copiers and image scanners include a line lighting device for lighting lines over a main scanning range of a paper surface. The line lighting device is a rod-like light guide contained within a case that has a light emitting unit (LED) fixed at one end, and is arranged so that light incident on an end face of the light guide is reflected within the light guide and emitted towards the paper from an exposed emitting face not covered by the case.
The light guide has to be fitted into the case in such a way that a gap between the light emitting unit and a light guide end face which opposes the light emitting unit is accurately maintained. To this end, Patent Document 1 records an arrangement in which a recess 102 is formed in an opening 101 at one end of a case 100 and a protrusion 104 is formed at one end of the a rod-like light guide 103 to engage with the recess 102 so that the distance between the light guide end face and an LED 106 of the light emitting unit is constant, as shown in FIG. 16.
The rod-like light guide 103 is easily fitted into the case 100 by firstly inserting the tip of the protrusion 104 into the opening 101 of the case 100. However, the presence of the protrusion 104 requires that the rod-like light guide 103 is inserted with the end not having the protrusion going first as shown in FIG. 17(a). Lastly, the protrusion 104 is engaged with the recess 102 as shown in FIG 17(b).
Patent Document 1: Japanese Patent No. 2999431
With the above-described conventional insertion method, surfaces over the entire length of the rod-like light guide may rub against the opening portion of the case, and be scratched. At scratched portions, light reflects in an irregular manner, adversely affecting the performance of the lighting device.
Also, great care must be taken when sliding the rod-like light guide, distal end first, into the case. Thus, the operation to fit the light guide requires both time and practice.